1. Technical Field
This disclosure generally relates to the detection of the presence or absence of objects tagged with transponders, which may, for example, allow the detection of medical supplies, for instance surgical objects during surgery.
2. Description of the Related Art
It is often useful or important to be able to determine the presence or absence of an object.
For example, it is important to determine whether objects associated with a medical procedure, for instance a surgery or child birth deliveries, are present in a patient's body before completion of the medical procedure. Such objects may take a variety of forms used in medical procedures. For example, the objects may take the form of instruments, for instance scalpels, scissors, forceps, hemostats, and/or clamps. Also for example, the objects may take the form of related accessories and/or disposable objects, for instance sponges, gauzes, and/or absorbent pads. When used in surgery, failure to locate an object before closing the patient may require additional surgery, and in some instances may have serious adverse medical consequences. In other medical procedures, such as vaginal child birth deliveries, failure to remove objects, for instance gauze or absorbent pads can lead to infections.
Some hospitals have instituted procedures which include checklists or requiring multiple counts to be performed to track the use and return of objects during surgery. Such a manual approach is inefficient, requiring the time of highly trained personnel, and is prone to error.
Another approach employs transponders and a wireless interrogation and detection system. Such an approach employs wireless transponders which are attached to various objects used during surgery. The interrogation and detection system includes a transmitter that emits pulsed wideband wireless signals (e.g., radio or microwave frequency) and a detector for detecting wireless signals returned by the transponders in response to the emitted pulsed wideband signals. Such an automated system may advantageously increase accuracy while reducing the amount of time required of highly trained and highly compensated personnel. Examples of such an approach are discussed in U.S. Pat. No. 6,026,818, issued Feb. 22, 2000, and U.S. Patent Publication No. US 2004/0250819, published Dec. 16, 2004.
Commercial implementation of such an automated system requires that the overall system be cost competitive and highly accurate. In particular, false negatives must be avoided to ensure that objects are not mistakenly left in the patient. Some facilities may wish to install a single interrogation and detection system in each surgery theater or room in which medical procedures are conducted, while other facilities may move an interrogation and detection system between multiple surgical theaters or other rooms. In either case, the overall system will require a large number of transponders, since at least one transponder is carried, attached or otherwise coupled to each object which may or will be introduced into a patient or subject during the medical procedure. Consequently, the transponders must be inexpensive. However, inexpensive transponders typically have a relatively large variation in the frequency of signals they emit, making it difficult to accurately detect the signals returned by the transponders. This may be particularly difficult in some environments which are noisy with respect to the particular resonant frequencies of the transponders. Rooms in hospitals in which medical procedures are performed tend to have increasingly larger amounts of electronic equipment, and hence are becoming notoriously noisy environments. Consequently, a new approach to detection of the presence and absence of transponder that facilitates the use of inexpensive transponders is highly desirable.